Integrated circuits (“ICs”) typically have several patterned thin-film metal layers separated by dielectric layers. Conductive vias are used to make electrical connections from one patterned metal layer to another. It is desirable to avoid parasitic capacitances for a variety of reasons, and “low-k” dielectric materials (i.e. materials having a low dielectric constant) are preferred. As used herein, “low-k” refers to dielectric material that has a relative dielectric constant less than 4, which is the nominal relative dielectric constant of silica.
Several types of low-k dielectric materials are based on silica, such as fluorinated silicate glasses (“FSGs”) or undoped silicate glasses (“USGs”). Many IC fabrication techniques have been developed to use FSG materials, such as chemical-mechanical polishing (“CMP”), via etch processes, and metallization processes. Other types of low-k dielectric materials are organic-based.
An example of an organic-based low-k dielectric material is the dielectric material resulting after processing SiLK™ resin. SiLK™ resin is available from the ADVANCED ELECTRONIC MATERIALS group of THE DOW CHEMICAL COMPANY, and is applied as in a fluid state. After the resin is cured, a porous dielectric matrix remains. Dielectric materials having relative dielectric constants as low as 2.6, and in some instances as low as 2.2, are obtained using SiLK™ material. For purposes of discussion, low-k dielectric materials that are applied to an IC wafer in a fluid state and then cured to provide solid dielectric material incorporated in the IC will be referred to as “fluid-based” dielectric materials.
While SiLK™-type materials have been developed to utilize typical IC fabrication apparatus and methods, the techniques for using organic-based low-k dielectric materials in ICs are often substantially different than those for using FSG or USG materials. For example, SiLK™ layers can be patterned. They are often cured for a relatively long time (24 hours) after patterning, which is not required with FSG or USG materials. If SiLK resin is used to form many layers of dielectric material in the IC, the after-patterning cure is typically repeated for each layer, adding to the process time, increasing work-in-progress, and often reducing throughput of the IC fabrication facility.
It is therefore desirable to provide techniques for utilizing fluid-based dielectric materials between conductive layers in an IC that avoids the multiple curing times of conventional techniques.